INDUSTRIAL PROGRESS DURING THE YEAR 1876. xxxix 



grade in January. The comparative dryness of the air is seen from 

 the fact that the average humidity throughout the year is about fifty 

 per cent. The observations at some of the high stations seem to 

 suggest that the minimum temperatures at an altitude of 7000 feet 

 are possibly higher than the corresponding minima in the low lands. 

 Among the stations showing a large rainfall we notice Kangra, where 

 the annual fall amounts to 110 inches, while at Simla and Dehra the 

 corresponding amounts are fifty and sixty inches. 



Professor Langley, in an article on the solar atmosphere, gives the 

 results of his measures of the distribution of heat and light over the 

 solar disk ; the absorption of heat takes place, he thinks, principally 

 in a thin stratum at the base of the chromosphere. The slightest 

 change in the solar atmosphere has an appreciable efifect on the ab- 

 sorption, so that we have here at hand a sufi^cient cause for those 

 variations in solar heat that geological observations seem to de- 

 mand. The absorption is also selective, so that the sun tends to 

 have a bluish tinge when the absorbing layer is thin, but to have a 

 reddish tinge at other times, affording us thus some rational hypoth- 

 esis whereby to explain the phenomena of variable stars. 



The influence of atmospheric moisture upon the absorptive jDower 

 of the atmosphere has been further illustrated by Hoorweg, who has, 

 by a renewed series of observations, conclusively shown the general 

 correctness of Tyndall's results, according to whom a small percentage 

 of vapor in the atmosphere increases enormously the absorption and 

 radiation of obscure heat, and moderates terrestrial climates. 



More recently still Lohse has, with great acumen, discussed the 

 observations of Tyndall, Magnus, and Wild, and has added an excel- 

 lent investigation of his own, showing that the effect of aqueous va- 

 por is by no means as decided as maintained by Tyndall. 



The relation of warm, dark heat rays to hydrogen and the atmos- 

 phere has been studied by Buff", of Giessen, who has repeated a series 

 of experiments bearing on the absorption of heat by the atmosphere, 

 and concludes that hydrogen is as nearly transparent to heat as a 

 vacuum, while dry air absorbs fifty or sixty per cent, of heat rays. 

 The assumption of Tyndall that the power of damp air to absorb 

 rays of heat coming from a dark source exceeds by fifteen to forty 

 per cent, the absorptive power of dry air is incorrect. It is correct, 

 however, to say that such heat rays as are not absorbed in dry air 

 can become absorbed, or do experience a very sensible diminution 

 when passing through damp air. 



Mendeleff endeavors, by means of Poisson's equation, to arrive at 

 formulae by which we may calculate the temperature of rarefied air 

 with a high degree of approximation. In reference to the expansion 

 of air by heat, he has shown that for pressures between 750 and 770 

 millimeters tlie coefficient of dilatation of the air is 0.00036843 for 1 

 degree of Centigrade. 



